Two kind of socialin: people focus or hobby focus
The service is not free
Groups are self-orgnized system in which global patterns emerge from local action and structure subseqeucent local acton. 

The challenge in this research in in mapping quantitative measurements of interactions based on network traffic to qualitative analyses of social relationship;it's easy to know what people are doing in the network, but it is harder to know why. - Sarita Yardi